this really depends on what you want. an iframe will be more integrated with the site and will allow for visitors to visit other pages easier, but an external link will probably look better. If you want to use iframes then id experiment, they're two good free ones in the marketplace, try to find out whats the best for you.

One thing you might want to do is ask on the posterous site/forums.

People probably integrate it all the time in there static sites...

Have a look here:
http://apidocs.posterous.com/

From a quick glance, it appears that the API will allow you to do a full integration without the need for an iframe.

Jon

Thanks for the replies.

I asked on the Posterous forum but so far no responses.

Jon - I looked at that link. Thanks. But API stuff is way beyond me and I wouldn't know how to begin.

I'm going to keep searching for a solution but since my client is so in love with twitter, I thought a really non-technical blog solution would be best. I'm even a little nervous about support issues if they try to use one of the blog addons for C5.

Aaron